Bidirectional Crosstalk Between Bladder Cancer Cells and Normal Fibroblasts Drives Phenotypic Reprogramming and Modulates Chemosensitivity

Bladder cancer is one of the most common malignancies worldwide and is marked by high recurrence rates, highlighting the urgent need to better understand the tumour microenvironment (TME). While the role of cancer-associated fibroblasts (CAF) in cancer progression and therapy resistance is well established, the contribution of normal fibroblasts (NF) remains underexplored. Here we dissect bidirectional interactions between bladder cancer cells and NF using indirect (conditioned media) and direct co-culture systems. Fibroblast-conditioned media (FCM) reduced proliferation in RT112 and T24 cells while accelerating cell migration. Immunofluorescence revealed a cadherin remodelling with increased N-cadherin and reduced E-cadherin after FCM exposure. On the stromal side, NF acquired CAF-like features within 48 h, with SMA and FAP increases evidenced by imaging in conditioned media and confirmed by flow cytometry in direct co-culture. In addition, direct co-culture reduced mitomycin C (MMC) efficacy in a fibroblast-ratio dependent manner in both cancer cell lines. It suggests that fibroblast composition in the TME may influence individual variability in treatment response. These findings highlight a significant role for NF in modulating bladder cancer behaviour and therapeutic resistance, supporting the need to consider fibroblast-cancer interactions in developing more effective treatment strategies.